1. Field of the Invention
The present invention relates to a digital TV receiver, and more particularly, to a digital TV receiver for recovering a symbol clock from received data.
2. Discussion of the Related Art
An advanced television systems committee (ATSC) 8 VSB (Vestigial Side Band) transmission system proposed by most current digital transmission systems and a US directed digital TV transmission mode loads data only in a transmission signal to increase an effect of a frequency. That is, clock information needed for data recovery at a receiving party is not transmitted. Therefore, the same clock as that employed during the transmission should be generated among the received signals having only data to recover the data at the receiving party. A symbol clock recovery performs the role.
The carrier recovery performs the carrier recovery by detecting a pilot signal included in the transmitting signal. If the carrier recovery includes FPLL (Frequency Phase Locked Loop), the FPLL simultaneously performs a FLL (Frequency Locked Loop) process and a PLL (Phase Locked Loop) process, the FLL process removing frequency difference between the carrier component of the receiving signal and standard carrier component of the receiver itself, and a PLL process removing phase difference of the two carrier signals from which the frequency difference is removed.
In this case, if the carrier recovery and symbol clock recovery are coupled in order, the symbol clock recovery is not totally removed from the carrier recovery and is influenced by a remained frequency and phase error flowed in because efficiency of the carrier recovery largely influences on efficiency of the symbol clock recovery, and that gives bad influence on the total performance of the symbol clock recovery. That is, when the carrier recovery is not completely performed at the carrier recovery member, the frequency and phase error differences between the carrier signal and the standard carrier signal are outputted to the symbol clock recovery, the carrier signal employed by the receiver. Therefore, the symbol clock recovery carries out symbol clock recovery from the signal, and it is difficult to normally recover the symbol clock.
The reason why the symbol clock recovery is located at an end of the general carrier recovery is that the symbol clock recovery is designed under an assumption that the role of the carrier recovery is completed. Therefore, if the carrier recovery is not completely performed, the symbol clock recovery is not performed as well.